The present invention relates to an automatic transmission for a vehicle, which has a hydraulic controller, and a method of manufacturing the automatic transmission.
Generally, automatic transmissions mounted on vehicles include a transmission mechanism having a hydraulic actuator of a frictional engaging element for example, a transmission case accommodating the transmission mechanism, a hydraulic controller for controlling application and discharge of oil pressure to and from the hydraulic actuator, supply of lubricating oil to various parts inside the transmission case, supply of oil to a torque converter, for example.
The hydraulic controller of such an automatic transmission commonly has valve insertion holes to which solenoid valves and spool valves, which constitute a hydraulic control circuit, are inserted, and a valve body formed with oil paths communicating with the valve insertion holes.
As JP2013-253653A discloses, conventionally, a valve body of a hydraulic controller is formed by stacking a plurality of layers of valve body structuring members while sandwiching a separating plate between mating surfaces of the adjacent layers, and fastening them with a plurality of bolts to form units. Each layer of the valve body structuring member is molded by, for example, die casting of aluminum. Thus, high-quality and efficient mass production has become possible.
Valve insertion holes are formed by processing the molded valve body structuring members, and oil paths are formed by the same molds of the valve body structuring members when molding the valve body structuring members. Therefore, each oil path is formed in a valve body structuring member to extend along a mating surface with another valve body structuring member, provided that the oil path opens to the mating surface over an entire length thereof for the sake of convenience in demolding.
In each layer of the valve body structuring member, the opening of the oil path in the mating surface is closed by the separating plate or communicates, through a communication hole formed through the separating plate, with an oil path of an adjacent valve body structuring member via the separating plate.
The valve body structured as above is attached to an outside of a transmission case which is also molded by, for example, die casting of aluminum. Although the valve body is generally fixed to a lower surface of the transmission case by bolts and accommodated inside an oil pan attached below the transmission case, it may alternatively be attached to a side surface or an upper surface, for example, of the transmission case.
The oil paths formed in the valve body communicate with oil paths formed in the transmission case, through communication ports formed in a joining surface of the valve body with the transmission case. Thus, the oil paths of the valve body communicate with an oil-pressure source (e.g., oil pump), a hydraulic actuator of a transmission mechanism, lubricated parts inside the transmission case, and various parts which are applied with oil pressure (e.g., various parts of a torque converter) through the oil paths of the transmission case.
Further, in the case where the valve body is accommodated inside the oil pan, a discharge port of an oil strainer provided inside the oil pan is connected with a suction port formed in a lower surface of the valve body. Thus, by actuating the oil pump, oil stored in the oil pan is supplied to the oil paths of the valve body through the oil strainer.
However, since the conventional valve body formed with the oil paths by the molds is formed by stacking the plurality of valve body structuring members so as to seal each opening formed over the entire length of the oil path for the sake of convenience in the demolding as described above, the entire valve body easily increases in size and weight. Further, to secure a sealing ability at the mating surfaces, a large number of bolts are used to fasten the valve body structuring members with each other and, accordingly, a large number of bosses having a bolt hole are provided to the valve body structuring members, which also causes an increase in the size and weight of the valve body.
Since valve bodies that easily increase in size also project outside the transmission case, a size of the entire automatic transmission also increases. Therefore, there is room for improvement in the mountability of the automatic transmission in the vehicle. Especially, in the case where the valve body and the oil pan are attached below the transmission case, the oil pan is increased in size to an extent that it can accommodate the valve body and projects downward from the transmission case. Thus, a dimension of the automatic transmission in the vertical direction of the vehicle increases and the mountability of the vehicle degrades even worse. Additionally, since the heavier valve body is attached to the transmission case as above, the weight of the entire automatic transmission also increases, which causes fuel performance degradation of the vehicle as well.
Furthermore, the conventional automatic transmission in which the valve body is formed by coupling the plurality of valve body structuring members to each other and attached to the transmission case, also has an issue where the number of components and assembling processes become large.